[SYCL][L0] Rework how we maintain per-thread queue groups

[smaslov-intel]

No description provided.

[smaslov-intel]

This code was doing wrong it used the same ZeQueues for the new entry so it is then was destroyed multiple times causing a segfault. Now, without per-thread setting we don't even create multiple entries, and we do per-thread then the new entry is properly initialized here: https://github.com/intel/llvm/pull/8896/files#diff-1f19baf7cc76d94bf4a1819c81e7b34292fb3ce215cd50873e8c9236cc73601cR501

[rdeodhar]

This feature was for immediate command lists only. So the zeQueues should have been unallocated. Have you extended it for command queues also?

[rdeodhar]

So now the vector of ZeQueues is now separate for each entry?

[smaslov-intel]

See here, new entries are initialized with null: https://github.com/intel/llvm/pull/8896/files#diff-1f19baf7cc76d94bf4a1819c81e7b34292fb3ce215cd50873e8c9236cc73601cR501

[smaslov-intel]

It is still for immediate command-lists only, but it is safer to initialize ZeQueues to null for safety

[rdeodhar]

But that value should have been a null, and the zecommandqueuedestroy should not have been called. But it did get called, which means that the vector of zequeus has to be explicitly set to nullptrs. OK.

[smaslov-intel]

it was nullptr but then a call togetZeQueue created a non-null one: https://github.com/intel/llvm/pull/8896/files#diff-15dd1eb076d2164bd9e87d9057f05f652a716498e8cdf5975e564c65309a0985L2843

That non-null value was then copied to yet a new entry created for another thread.

[rdeodhar]

The perThread and getNative don't mix well. Say you have a queue that uses multiple cmd lists, one per thread. Someone calls getNative, makes his own queue from it and assumes that a sync on that queue is also a sync on the original queue. But it isn't because only one cmd list will be synch'ed.

[smaslov-intel]

Right, but the failure was even without per-thread requested. We still created multiple redundant entries, which additionally held the same queues. I don't think that syncing a queue returned by a get_native() gives any guarantees about the entire SYCL queue being synced.

[rdeodhar]

That insert was supposed to be "insert if not found".